As a physical therapist, I use anatomical terms like “pelvic floor” all the time. Recently, though, I’ve had several patients ask me just what the pelvic floor is. Is it a muscle? An organ? A membrane? I’m realizing that when I say “pelvic floor” patients may not know what I mean. If that’s you, and you’re interested in finding out, please read on.
The pelvic floor is quite literally the floor or the bottom of the pelvis. The pelvis is the bony structure that connects our legs to our spine. The bones are shaped like a bottomless bowl. What forms the bottom of the bowl is the pelvic floor. The pelvic floor consists of 3 layers of muscle, the nerves and blood vessels that feed and drain those muscles, and the connective tissue that binds everything together.
Below is a picture of the deepest layer of pelvic floor muscles. It is a simplified picture, but it provides a basic view of where the pelvic floor lies within the body. In life, we would also see nerves, connective tissues, arteries, veins, lymphatic vessels, internal organs, and other nearby muscles. The image shows the pelvic floor of someone born with a uterus and ovaries, but it is relevant to those born with a penis and testes too.
The front opening looks large and square. In real life, it’s two openings. A small opening in the very front for the urethra, where urine exits the body, and a larger vaginal opening. In those born with a penis and testes, the opening in front is smaller and for the urethra only. The circular opening in the picture is the anus. Other areas that appear to be openings in the picture really are not. They are areas where non-related anatomical structures have been removed so you can better see the pelvic floor. This deepest layer of the pelvic floor plays a major role in the support of the pelvicorgans – the rectum, bladder, and uterus if present. These organs are also connected to the walls of the pelvis or to the spine through ligaments. The bladder, for example, is attached to the front wall of the pelvis by the pubovesicular ligament.
Those born with a vagina
This next picture shows the most superficial muscles of the pelvic floor in a person with a vagina. In the image, bone is depicted in white, erectile tissue in blue, muscle in red, and mucus membrane in pink. The bone marked “IT” and its counterpart on the opposite side are the ischial tuberosities, sometimes called sit bones because they’re the bones we sit on. Toward the top of the photo is the pubic bone. Below the pubic bone is the clitoris, and below that the urethra.
The muscles that form the most superficial layer of the pelvic floor, the layer that’s closest to our skin, are labeled “BC” for bulbocavernous, “IC” for ischiocavernosus, “STP” for superficial transverse perineal, and “EAS” for external anal sphincter. Encased in the BC and IC is erectile tissue that shunts blood to the clitoris. This erectile tissue is present on both sides of the body even though the model only shows it on one side. The BC also acts to close the vagina and urethra. The STP provides stability to the perineum, marked “PB” for perineal body below. The perineal body is the muscular attachment point between the vagina and anus. If it’s not stable, the muscles that attach to it will not function as they should. The superficial transverse perineal muscle and the bulbocavernosus are the muscles that are cut during episiotomy or may tear during vaginal childbirth. In grade 3 perineal lacerations, part of the “EAS” or external anal sphincter muscle is torn. In grade 4 perineal lacerations, the tear extends all the way to the rectal mucosa, the pink area just beneath the “EAS”.
Image 1
BC: Bulbocavernosus Muscle
C: Clitoris
DTP: Deep Transverse Perineal Muscle
EAS: External Anal Sphincter
ET: Erectile Tissue
IC: Ischiocavernosus Muscle
IT: Ischial Tuberosity
LA: Levator Ani Muscles
OI: Obturator Internus Muscle
STP: Superficial Transverse Perineal Muscle
The image does not show the connective tissue, or fascia, that also forms the superficial pelvic floor. Each muscle fiber is surrounded by fascia called the endomysium. Each fascicle, or group of muscle cells, is also surrounded by fascia called the perimysium. The muscle as a whole is surrounded by fascia called the myomysium. Finally, the fascia of each muscle blends into the fascia of the muscles around it or forms a tendon, connecting the muscle to bone. Fascia is important because it provides support for muscles, nerves, arteries, veins, organs, . . . really all body structures. In fact, people with loose fascia including those with connective tissue disorders such as Ehlers Danlos Syndrome, are more likely to have pelvic organ prolapse than are those with normal fascial tone. The fascia of the superficial layer of the pelvic floor is often called the superficial pelvic fascia.
The middle layer of pelvic floor muscles consists of the “DTP” or deep transverse perineal muscle, shown in image 1 above. The DTP works with the superficial perineal muscle to stabilize the perineal body. The middle layer of pelvic floor muscles also includes muscles that are either not shown or not shown well in image 1. The urethravaginalis muscle runs deep to the bulbocavernosus and helps it close off the urethra and vagina. Also closing off the urethral opening to help maintain urinary continence are the internal urethral sphincter and the compressor urethra muscles. The connective tissue of this layer is often called the urogenital diaphragm or the perineal membrane.
Those born with a penis
The next images show half of the pelvic floor of a person born with a penis. The first gives a side view that allows us to see how the pelvic bones and organs relate to the pelvic floor. The puborectalis muscle, part of the levator ani muscle group of the deep pelvic floor is shown below, as is the external anal sphincter.
The next image shows the superficial pelvic floor in a person with a penis and scrotum. The model pictured does not show erectile tissue, but erectile tissue is present and is encased in the bulbospongiosus and ischiocavernosus muscles. If those muscles are too tight or too weak, erectile function may suffer. The model also omits showing the striated urethral sphincter muscle that is present in the intermediate layer of the pelvic floor and aids with urinary continence. And finally, the image does not show the pelvic nerves or the connective tissue or fascia that is also part of the support structure of the pelvic floor.
BS: Bulbospongiosus Muscle
DTP: Deep Transverse Perineal Muscle
IC: Ischiocavernosus Muscle
STP: Superficial Transverse Perineal Muscle
Summary
So, when physical therapists talk about the pelvic floor, we aren’t talking about one specific muscle or structure. We’re talking about a group of muscles along with their nerves and connective tissues. Together these component parts play an important role in supporting the pelvic organs, controlling urination and defecation, stabilizing the core, pumping excess fluids out of the pelvis, and allowing for sexual function.
